Phase change materials reliably change phase at a predetermined temperature to provide a repeatable temperature measurement. As heat is applied to a solid-liquid phase change material within a phase change cell, the temperature of the phase change material in a solid phase will rises until the material reaches its phase change temperature (the melting temperature). At this point, the phase change material will continue to absorb a significant amount of heat at a virtually constant temperature until all the material is transformed to the liquid phase. Likewise, the phase change material will release its stored latent heat energy at its phase change temperature in the transition from a liquid phase to a solid phase. This characteristic flattening of the temperature response of the phase change material during heating or cooling provides a stable, reliable indication of temperature.
High precision phase change cells are devices that encapsulate phase change materials and yield a measurable phase change temperature during a heating or cooling cycle. Such phase change cells can be used in a variety of contexts and environments to assist in temperature calibration. For example, climate systems, such as space-based climate systems utilizing optical instruments, must be periodically calibrated in order to provide accurate data. Without regular calibration, such instruments are subject to temperature drift that may impact the accuracy of the instruments. Various other climate systems require certain components to be accurately maintained or moved towards certain temperatures in order for these components to be properly operated and controlled.
Temperature readings provided by a phase change cell during a phase change can be used to calibrate temperature sensors. However, designs of existing phase change cell enclosures suffer from limitations in delivering accurate temperature measurements. Typically, the chamber inside the phase change cell containing the phase change material is partially filled with a gas pocket. Especially in micro-gravity environments, the location of the gas pocket within the chamber cannot be controlled and potentially could be adjacent to the wall of the phase change cell where the temperature sensor is located. This situation may result in an inaccurate reporting of the phase change material temperature, because the temperature of the gas pocket is measured instead of that of the phase change material.
Further, in some contexts it is desirable to measure the phase change temperature of several different materials in order to develop a temperature curve to support more accurate calibration using curve fitting. However, this technique generally requires a more complex phase change cell structure involving multiple chambers to separately house different phase change materials, together with corresponding controls and sensors.